FLARE STACK ANALYSIS AND EMISSIONS CONTROL UNDER THE NEW MACT REGULATIONS
AUTHORS : DAVID FAHLE , SERVOMEX ' S HYDROCARBON PROCESSING MARKET SECTOR MANAGER AND ZARINA STANLEY , GLOBAL MARKETING MANAGER HYDROCARBON PROCESSING
MEASURING EFFICIENT COMBUSTION
The excursion of gases from a flare stack can be very quick , inconsistent , and made up of a variety of components . This is particularly the case in petrochemical plants , making them harder to monitor than refineries .
The steam-to-vent-gas ratio required can be very different for each gas - for example ethane requires 0.1 to 0.15 kg of steam per kg of gas , whereas butadiene requires the ratio to be nine times higher , between 0.9 to 1.0 kg .
Efficient regulation therefore needs continuous compositional analysis to ensure the steam-to-vent-gas ratio is maintained at its most efficient level and complies with the CE target . A device capable of this continuous compositional analysis can therefore provide a much better understanding of the overall flare performance .
Three technologies exist to help measure the efficiency of flare stack combustion : Gas Chromatography , Calorimetry , and the innovative Tunable Filter Infrared technology used in Servomex ’ s SpectraScan 2400 / H2Scan system .
Gas Chromatography ( GC ) has been used extensively in the past , as it meets measurement requirements for most flare applications . However , GC has an issue with cycle time : a complex analysis can take up to 15 minutes . Also , temperature , density and flow can all affect GC measurements .
A calorimeter works in a different way , by burning the sample and taking a measurement of the temperature . However , it does not inform you what the composition of the sample may be . While the reading can be continuous , there is also some latency .
Servomex ’ s system , comprising the SERVOTOUGH SpectraScan 2400 and H2Scan working in combination , gives a continuous reading with a good compositional measurement . It measures 14 components , giving an overall British Thermal Unit ( BTU ) value and individual component values .
This completely integrated system has no carrier gas and needs no recalibration or adjustment , so there are few , if any , parameters to affect the sample .
The SpectraScan 2400 is a Tunable Filter Infrared analyzer which can accurately separate light hydrocarbon components in the C1 to C6 range . With a unique wavelength-scanning spectrometer , fast analysis is performed for these light hydrocarbons , as well as H 2S if required .
Sampling is made continuously using a flow-through system , which makes it suitable for online , unattended operation , while the analyzer , having no carrier gas or recalibration requirements , does not need high maintenance .
The H2Scan integrates simply with the SpectraScan , using non-depleting thin film technology to provide a direct , realtime hydrogen measurement that is not cross-sensitive to other gases . Hydrogen is commonly vented more than any other gas , so is always present in flare lines .
The combination of these two technologies provides a detection system that is simpler and superior to traditional analysis , with considerably lower implementation and product lifetime costs .
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